Inflatable evacuation slides are commonly used on passenger-carrying aircraft to provide means for rapid evacuation of passengers in the event of an emergency. The descent of evacuees on an inflatable evacuation slide is in many respects governed by the sliding angle formed between the sliding surface or the floor of the inflatable and the ground. At the shallow sliding angle, in view of the slow rate of descent, the evacuation may not be accomplished fast enough. At the sliding angle above the optimal range, the sliding surface may be too precipitous and evacuees will be reluctant to utilize the slide. However, even if they proceed, injuries might result upon impact with the ground. The problem facing the modern aviation industry is that the same slide is designed and used for both normal sill height, with all landing gear in the extended position, and for the adverse sill height with one or more landing gear or other portions of an aircraft collapsed or damaged. In the latter condition, certain portions of the fuselage can be significantly raised or lowered and the slide should have extra length to accommodate such height variations. Since at the normal sill height, such slide extends further away from the aircraft, situations with a shallow sliding angle can be encountered. This poses two problems. One of such problems is that the speed of the egress of the evacuees can be very slow, so that the passengers cannot be evacuated fast enough within the required short time limits. The other problem associated with a shallow sliding angle is that instead of being transferred into the speed of the evacuees going down precipitously, in view of the lower speed of their movement, the load on the slide actually increases. In such condition, the structure of the slide requires the strength substantially greater than normal. For this purpose, the strength of the longitudinal support beams has to be increased by, for example, providing supplemental tubes underneath the slide. Such inflatable arrangements are expensive to manufacture and less reliable in operation.
Another important issue related to the design of the aircraft slides is that each slide is tailored not only to a particular model of aircraft, but also to a specific door of the same aircraft. This is because in case of emergency landing, each door is at a particular adverse sill height, depending on the condition of the aircraft. For instance, when an aircraft on the ground loses one landing gear or an engine, it might have a nose-up position in which the maximum sill height of front doors would substantially exceed the normal sill height thereof. Therefore, slides utilized at the forward doors of aircraft should require substantially greater length than those at the aft doors.
In view of emergency situations, it is quite difficult to predict the height of a door of aircraft and the value of the sliding angle. This is because one or more of the landing gear and engines of the aircraft can be damaged or collapsed such that the aircraft's fuselage itself may be canted. The height of the escape doors varies significantly depending upon the type of plane and the character of the accident. For example, in view of large size engines requiring longer landing gear, new aircraft are actually positioned higher off the ground than former models. This leads to more extremes in terms of the ranges between normal and adverse sill heights. One of the examples of such aircraft is Boeing 777 requiring a very long slide for the forward door. Such arrangement results in a shallow sliding angle for this door at the normal sill height.
Aircraft often carry hundreds of passengers and safety regulations require that all passengers must be removed from the aircraft in the shortest possible period of time. Thus, all doors, including those furthest from the ground, must be utilized with the result that each must be provided with an escape slide designed to operate efficiently at any height and at any angle.
One example of resolving problems associated with variable sill height of aircraft has been described by U.S. Pat. No. 4,246,980 which the present case incorporates by reference.
Thus, it has been long felt an unsolved need for a simple and reliable inflatable evacuation slide for an aircraft capable of accommodating not only the normal sill height, but also a maximum adverse sill height thereof, while providing safe and expeditious evacuation of passengers.